The use of implantable drug infusion systems is well-known. These systems provide steady, long-term delivery of drug therapy to the human body. They also eliminate the need for frequent intravenous drug injections. Each system typically includes a refillable drug reservoir and flow control device for regulating the drug delivery rate.
One form of drug infusion system incorporates an implantable pump such as that disclosed in U.S. Pat. Nos. 5,445,616 and 5,575,770. The subject matter of both patents is incorporated herein by reference. Pump-based systems provide constant flow of drug to the patient at very low rates. These pumps may be fixed rate pumps or programmable pumps. In the case of fixed-rate, adjustment of the delivery rate and therefore the drug dosage may not be altered. In case of programmable pumps, reprogramming of the pump controller by a physician is required for changes in pump rate.
There is a current trend towards providing some degree of patient control in implantable drug infusion systems. Clinical studies show that actual drug usage may be reduced if a patient believes that he or she has some degree of control over drug dosage. A terminally-ill patient who has no ability to control or self-administer a drug will frequently insist on additional dosage at each visit to a physician as a precaution against exhaustion of the drug supply before the patient's next office visit. In addition to these patient psychological aspects, there are added benefits of patient control. For example, in progressive diseases, the development of breakthrough pain may require immediate increase in drug dosage. Similarly, a diabetic patient may need to tailor insulin dosage to maintain blood glucose levels through a changing diet. The ability to self-administer drug therapy may therefore reduce the number of office visits and provide immediate drug dosage increase when needed.
There have been prior efforts to provide drug infusion systems that offer patient controlled dosage features. One known form of drug infusion system which includes patient controlled dosage features is a drug infusion pad, such as that disclosed in U.S. Pat. No. 5,085,644, which permits a patient to self-administer drug therapy. Typically, this patient control of dosage is in the form of a deformable chamber which may be compressed by the patient to deliver an intermittent supply of drug to the body. The infusion pad is implanted subcutaneously, usually over the rib cage to provide support against the forces of a patient's fingers compressing the reservoir. Known drug infusion pads, however, only provide for intermittent delivery of drug therapy and are therefore undesirable in applications where a steady flow of drug is desired. The patient must continuously activate the infusion pad to receive medication. For example, U.S. Pat. No. 5,085,644 discloses a patient-controlled infusion device which utilizes a deformable pumping chamber to permit a patient to intermittently administer a supply of drug from a main reservoir. The disclosed device utilizes a fluid flow restrictor to limit the recharge rate of the pumping chamber.
There is a yet unaddressed need in the medical field for a drug infusion system which offers the benefits of both fixed-rate delivery systems and patient control of dosage. Such a system would find application in therapy delivery for example, for cancer patients, who may need a fixed rate of drug delivered constantly and the ability to administer themselves a bolus of drug when "breakthrough" pain occurs. Similarly, a diabetic patient may need, in addition to a steady supply of insulin, an additional dosage when the patient's diet has resulted in a lower than anticipated blood glucose level.
It would therefore be desirable to provide a drug infusion system which provides patient-control features in addition to the advantages offered by fixed rate delivery systems.